1. Field of the Invention
The invention relates to image synthesizing apparatus and method for synthesizing images in accordance with an α value showing an opaqueness degree and, more particularly, to image synthesizing apparatus and method for enabling an α value of a desired shape in a desired position to be rewritten to a desired value in a desired range.
2. Description of the Related Arts
Development of an image processing chip for processing image data transmitted by digital CS (Communication Satellite) broadcast, digital BS (Broadcast Satellite) broadcast, or digital CATV (Cable Television) broadcast is being progressed. Such an image processing chip has a motion image processor, a display processor, a BitBLT (Bit Block Transfer) engine, a JPEG (Joint Photographic Experts Group) engine, and the like. A host CPU and a memory are externally connected to such an image processing chip.
Motion image data is supplied to the motion image processor. The motion image processor executes format conversion or the like to the motion image data. The motion image data in a format comprising an opaqueness degree α, luminance Y, and color differences Cr and Cb is outputted from the motion image processor. The motion image data from the motion image processor is sent to the display processor and a background image such as OSD (On Screen Display), EPG (Electronic Program Guide), capture display screen, or the like is synthesized to the motion image by the display processor. When the images are synthesized as mentioned above, α blending is executed.
The α blending is intended for synthesizing a plurality of images in accordance with transparency and an α value is used as a value indicative of the opaqueness degree. For example, when the α value is equal to “1”, the image is opaque. If the image whose α value is equal to “1” is synthesized, the under image cannot be seen in an overlapped position of the images. On the other hand, when the α value is equal to “0”, the image is transparent. If the image whose α value is equal to “0” is synthesized, the under image shows through in an overlapped position of the images. When the α value is equal to “0.5”, the image is translucent and an image in which the top image and the under image are evenly mixed is seen in an overlapped position of the images.
The α blending for synthesizing the images in accordance with the α value as mentioned above can be fundamentally constructed by a multiplier 201 for multiplying one image data by the α value, a multiplier 202 for multiplying the other image data by a (1−α) value, and an adder 203 for adding an output of the multiplier 201 and an output of the multiplier 202 as shown in FIG. 18.
Owing to such a construction, now assuming that the image data from an input terminal 200 is set to G1 and the image data from an input terminal 204 is set to G2, the following arithmetic operation is executed.α·G1+(1−α)·G2Thus, an image which is outputted from an output terminal 205 becomes an image in which the inputted image data G1 and G2 have been weighted by the opaqueness degree according to the α values and synthesized.
FIG. 19 shows an example of a conventional blender which is installed in a digital image signal processing chip.
In FIG. 19, a memory 251 and a host CPU (Central Processing unit) 252 are provided out of the image signal processing chip in which a blender 253 is installed.
Image data which is obtained by decoding a reception signal of, for example, the digital CS broadcast, digital BS broadcast, digital CATV broadcast, or the like is outputted from a motion image processor 254 arranged in the image signal processing chip. The image data has a format of, for example, (α, Y, Cr, Cb). The image data is supplied to motion image input units 221 and 222.
Image data serving as background images is read out from the memory 251 and sent to background image reading units 223 and 224. The image data stored in the memory 251 has a format of, for example, (α, Y, Cr, Cb).
The image data inputted to the motion image input units 221 and 222 and the image data read out to the background image reading units 223 and 224 are supplied to an α blending synthesizing unit 235. All of the image data inputted to the motion image input units 221 and 222 and the image data read out to the background image reading units 223 and 224 are synchronized by a sync control unit 225.
The α blending synthesizing unit 235 synthesizes the image data from the motion image input units 221 and 222 and the image data from the background image reading units 223 and 224 in accordance with the α values.
In the α blending synthesizing unit 235, the image data inputted to the motion image input units 221 and 222 and the image data read out to the background image reading units 223 and 224 are synthesized on the basis of the α values. The image data synthesized as mentioned above is outputted from output terminals 236 and 237.
As mentioned above, in the α blending, the image data is synthesized on the basis of the α value showing the opaqueness degree. When the α value is equal to (α=1), the image is opaque. When the α value is equal to (α=0), the image is transparent. If the α value can be updated to a desired value in a desired range, the image in a desired area of the image can be gradually visualized or gradually widened or narrowed like a wiping process.
In the conventional blender, however, a function such that the α value of a part of the image is changed in a range shown in an arbitrary shape with respect to each of the inputted images is not provided. The process for rewriting the α value can be realized by the software process also in the conventional blender. However, if it is tried to execute the process for rewriting the α value by software, the operations for reading out the image data stored in the memory 251, directly rewriting the α value in a software manner by using the host CPU 252, thereafter, writing the image data into the memory 251, and reading it out again from the memory 251 by the background image reading units 223 and 224 are necessary, so that a burden on the host CPU 252 is increased.
The image data which is inputted to the motion image input units 221 and 222 is the motion image data formed by decoding the reception signal of, for example, the digital CS broadcast or digital BS broadcast and is not stored into the memory 251. Therefore, with respect to the image data of the motion image which is inputted to the motion image input units 221 and 222, it is difficult to partially rewrite the α value by software.